The production of ethyl alcohol in dry-mill ethanol plants utilizing grains as feedstock is a major fuel alcohol in the U.S.A. A plant utilizing corn as feedstock can typically produce 2.7-2.8 gallons of ethanol and 17-18 lbs. of distillers grains with solubles (dry basis) per bushel of corn. While ethanol is the core product and the reason the processing plant exists, the byproduct, distillers grains with solubles, is also an important and significant revenue stream for an ethanol plant. Beyond increasing or improving the efficiency ethanol production and yield from corn, optimizing the value and dollar return of the byproduct stream is critically important to maximize profitability.
However, the dramatic increase in ethanol production from corn since 1999 has led to a faster growth in distillers grains supply compared with demand. The over-supply compared with demand has caused a reduction in price of distillers grains equal to 50% when expressed on a corn equivalent basis. That is, distillers grains sold for 1.2 times the price of corn ten years ago but now sell for 0.7 times the price of corn.
One proposed method of increasing the demand of the byproduct is to remove the crude oil contained within it for use in other industrial processes such as biodiesel production. A lower oil ethanol byproduct could be used at higher inclusion levels in livestock diets. Each bushel of corn that may produce 2.7 gallons of ethanol, also contains approximately 2 lbs. of corn oil. Further, a typical 100 million gallon per year corn-to-ethanol plant will discard approximately 40,000 short tons of crude corn oil per year in the distillers grains byproduct. When distillers grains are used as feed, at higher levels of inclusion of the byproduct the oil content in the byproduct begins to have deleterious effects on the animal, such as reduced milk fat production in dairy cows, reduced conception rates, soft fat in pork and bacon due to a high level of unsaturation, as well as reduced feed intake and weight gain in beef feedlot cattle. Therefore, there are significant advantages to removing the oil from the byproduct, such as increasing the level of effective inclusion in livestock diets and allowing the oil to be directed toward higher value industrial processes or feed markets.
However, when a significant amount of oil is removed from distillers grains, the digestible energy content of the feedstuff is also reduced as oil contains 2.25× the gross energy compared with carbohydrates. This results in a distillers grains feedstuff that may be used at higher inclusion levels but has a much reduced digestible energy content compared with the full oil distillers grains.
Solutions have been attempted to remove oil from grains. For example, soybeans, canola, sunflowers, cottonseed, peanuts, and other commodities are valued for their oils. Technologies, such as solvent extraction or extrusion, exist for the efficient and economical removal of oil from these commodities. However, these same technologies are generally applied to corn at the front end of an ethanol production process, that is, prior to distillation. Unfortunately, the oil content in corn grain is typically only between 3.5% and 4.0% and removing it from the grain is not very cost effective. An alternative solution is to fractionate the germ from the rest of the corn kernel for oil removal, as the germ contains approximately 25% oil. It is by this fractionation method that commercial corn oil is typically obtained in the wet milling industry. Unfortunately, in dry milling, corn components such as germ, pericarp and endosperm do not separate easily or cleanly, as compared to wet milling processes. For example, the germ can be separated by a dry milling process, however it is at the expense of some starch loss which results in lower ethanol plant productivity and profit.
In addition to the current issues in removing oil, in the ethanol production process, thin stillage typically can only be condensed to a total solids content ranging between 20% and 30%. Further, the gums and waxes in the thin stillage cause the solubles to become very viscous when it is condensed and these components often cause fouling of condensers. Further, while it is possible to use a high speed centrifuge to remove crude corn oil from thin stillage, the industry has only been able to achieve between 25%-80% removal of total oil in thin stillage due to the presence of these gums and waxes which are bound with the oil and are loathe to relinquish their bonds. At best, solutions to remove or separate crude oil in thin stillage necessitate the use of very high speed, costly centrifuges to recover a portion of the oil as the gums within stillage bind the oil. Moreover, the 25%-80% recovery of total oil in thin stillage is equal to only approximately 32% of the total oil available in whole stillage (40% of the oil from whole stillage present in thin stillage multiplied by 80% recovery).
Separation of oil from the grains, which constitutes a majority of the oil, cannot typically be accomplished by centrifugation because the oil is still bound within the germ. Therefore, solutions often include extraction methods. Typical extraction methods for oilseeds include solvent extraction with organic solvents such as hexane, benzene, ethanol, methanol and others, as well as extruding techniques which apply very high pressure and temperature to the material to ‘squeeze’ the oil out. Unfortunately, these methods are high cost compared with the relatively low amount of oil contained within the distillers grains (about 7.5% on a dry basis) and often include toxic chemicals. In addition, solvent extraction is not oil-specific but also extracts other components soluble in organic solvents, such as the gums which are also present in thin stillage, resulting in a crude oil with a high level of impurities requiring further refining.
Accordingly, there is a need in the art to produce a distillers grains ethanol coproduct that can be used at higher inclusion rates in livestock diets without reducing animal production or performance and that has significantly reduced oil content and increased digestible energy.
Further, there is a need in the art to more efficiently extract and reduce the oil content of distillers grains byproduct in a dry mill ethanol plant.
Further, there is also a need to increase the digestible energy content and nutritional value of distillers grains.
Further, there is a need in the art to produce a distillers grains byproduct with reduced oil content.
Further, there is a need in the art to produce a distillers grains product that can be fed at higher inclusion levels in livestock diets, thereby replacing more corn.